Some cities, most notably Chicago, dye their rivers green in observance of St. Patrick's Day each year.

On Saturday, the Codorus Creek turned white — but the change in color wasn't to mark the annual Yorkfest, which was held along the creek in York City over the weekend.

Rather, the murky white, almost gray tint was the result of limestone slurry that ran into the creek from a West Manchester Township cement-making facility, said Michael Helfrich, the Lower Susquehanna River Keeper.

Though unsightly, the addition of limestone slurry, a chalky, powder form of limestone, to the watery habitat doesn't appear to have killed off fish.

(Bil Bowden Photo)

On Sunday, Helfrich trekked down to a low-head dam near the West Philadelphia Street bridge in York City to check for any dead fish that might have collected there. Fortunately, there weren't any lining the banks.

"It didn't have an effect on the vertebrate population," Helfrich said.

Runoff: Helfrich said he got word of the change in the color of the creek by a York City councilwoman who happened to notice the white water near South Richland Avenue in Spring Garden Township.

Helfrich, who also serves on York City Council, was able to trace the discolored water back to Lehigh White Cement at 200 Hokes Mill Road in West Manchester Township.

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When he got to the plant on Saturday, representatives from the state Department of Environmental Protection and state Department of Transportation were also there investigating and working to keep limestone from further entering the creek, he said.

A PennDOT crew used stones and gravel to build a barrier near a stormwater drain to keep the slurry from entering the creek. Nearby, state DEP officials focused their attention on a large tank, Helfrich said as he showed pictures he had on his cellphone of the scene.

"But the material is so fine it just migrated" into the creek, he said.

Downstream: By 6 p.m. Saturday, the white water had made its way to the West Market Street bridge in York City. The murky water arrived just an hour after Yorkfest closed for the day on Saturday.

The creek through the city was still white when Helfrich checked it a final time about midnight. By 10 a.m. Sunday, it had returned to its brownish hue, just in time for Yorkfest to resume, Helfrich said.

Despite the limestone, the pH balance of the creek only increased by 0.02 percent, not enough to harm fish, Helfrich said he was told by a DEP official.

But the silt could have damaged or killed other wildlife, like mayflies and other small bugs that fish rely on for food, he said.